Communications Service providers commonly provide voice and data communications to each customer premise through a respective local loop between a Central Office and a demarcation point at the customer premise. The local loop is typically constructed as a pair of copper wires (commonly referred to as “tip” and “ring”, respectively), which may be either twisted together or flat untwisted. Traditionally, copper wire local loops were installed to carry voice communications (i.e. “Plain Old Telephone Service”, POTS). However, more recently, Communications Service providers have added data services using Digital Subscriber Line (DSL) services and its successors.
The demarcation point at the customer premise normally includes a splitter to separate the voice and data service signals. As may be seen in FIG. 1, a splitter 100 typically includes a line terminal 102, a phone terminal 104 and a data terminal 106. The line terminal 102 is configured to connect to the copper wire local loop Central Office, and so sends and receives signals associated with both of the voice and data services. The phone terminal 104 is configured to connect to customer owned telephone equipment, and so sends and receives signals associated with POTS services. The data terminal 106 is configured to connect to a customer owned modem and so sends and receives signals associated with data services.
Typically, the voice and data services signals are separated in the splitter 100 by low pass filter 108 which represents low impedance to POTS service signalling, while rejecting the higher frequency data service signals. This operation relies on recognition that POTS signalling typically involves only voice band frequencies (i.e. between about 200 Hz and 4 kHz), whereas data service signalling typically involves frequencies above 25 kHz. Accordingly, the low pass filter 108 can be designed to attenuate frequencies above 25 kHz, while passing the audio-frequency POTS signalling with low distortion. In the example of FIG. 1, the low pass filter 108 is provided as an LC-circuit comprising a pair of transformers 110, 112 and corresponding capacitors 114, 116. The data terminal 106 receives both POTS and data service signalling. However, the low-frequency POTS signalling can easily be rejected by a conventional modem utilizing high pass filter (not shown). By this means, the high frequency data signalling is removed from the POTS signalling by the low pass filter 108, and the low frequency POTS signalling does not significantly interfere with the high frequency data signalling.
A surge arrestor 118 is typically provided on the line side of the splitter 100 in order to dissipate voltage surges in the local loop, resulting from lighting strikes, for example.
In response to customer demand, communications service providers have progressively increased the speed of data services offered through twisted pair copper infrastructure. For example Very-high-bit-rate Digital Subscriber Line (VDSL) offers speeds of up to 52 Mbit/s downstream and 16 Mbit/s upstream, over a single flat untwisted or twisted pair of copper wires using the frequency band from 25 kHz to 12 MHz. Second generation Very-high-bit-rate Digital Subscriber Line (VDSL2) uses frequencies of up to 30 MHz to provide data rates exceeding 100 Mbit/s in both the upstream and downstream directions. At these high frequencies, Electro-Magnetic Interference (EMI) is an important factor limiting performance of the data service. A further limiting factor is the discrete capacitance of the surge arrestor 118, which tends to introduce interference into the data line. Typically, the discrete capacitance of the surge arrestor 118 is minimized by the use of Gas Discharge Tube (GDT) technology. However, GDT surge arrestors have a limited life, and their properties tend to change with each discharge cycle. Low-cost techniques for addressing the above issues would be desirable.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.